Accessory for external cardiac defibrillation, pacing and monitoring physiological signals/health data in the presence of electromagnetic interference

Abstract

This accessory adapts external cardiac defibrillation systems to enable safe defibrillation, pacing, and cardioversion inside the MRI bore with minimal effect on MR image quality. Commercially available external defibrillators are not designed to work in the MRI environment. An MR-compatible defibrillator is needed to safely perform cardiovascular MRI, in particular MR-guided interventional cardiovascular procedures, such as cardiac electrophysiology studies and cardiac catheterization. This accessory includes nonmagnetic defibrillator housing with MRI safety features, provides interface for MRI-compatible physiological monitoring, and optimizes defibrillator operation for the MRI environment. The accessory may include MRI-compatible modules for monitoring/recording electrocardiogram, blood pressure, pulse oximetry, and other physiological signals. It may also include a wireless transmitter and at least one module for electrical energy generation and/or stimulation.

The invention claimed is: 
     
       1. A system adapted for performing at least one operation selected from external cardiac defibrillation, cardiac pacing, and physiological monitoring in an MRI environment, said system comprising:
 a substantially nonmagnetic enclosure; 
 at least one sensor adapted for collecting at least one signal containing physiological data from the body of a subject; 
 an interface module in said nonmagnetic enclosure containing at least one EMI detector based on at least one time-domain feature having a different range of values for EMI compared with the range of values of said time-domain feature for said physiological data, to identify EMI within said at least one signal; 
 at least one processing element for minimizing said EMI within the time intervals in which said EMI is detected; 
 at least one adapter for connecting said body of a subject to at least one device selected from a defibrillator, a cardiac pacing device, and a monitoring device; and 
 at least one switch adapted for switching of the direction of the impedance-testing electrical current between at least two modes of operation selected from: (i) an EMI-free regime, in which said electrical current is redirected to an internal load; and (ii) a defibrillation regime, in which said electrical current is redirected to the defibrillation cable. 
 
     
     
       2. A system as set forth in  claim 1 , in which said at least one sensor is selected from: 1) a sensor of external magnetic-field strength, 2) an alarm activated in the presence of an external magnetic-field strength that exceeds a preset threshold, and 3) an ECG sensor, an electromyographic (EMG) sensor, an electroencephalographic (EEG) sensor, a blood-pressure sensor, a pulse-oximetry sensor, and an accelerometer sensor. 
     
     
       3. A system as set forth in  claim 1 , which further includes at least one system-control and signal-conditioning module, wherein said module contains at least one unit selected from an MRI-compatible ECG unit, an MRI-compatible blood-pressure measurement unit, an MRI-compatible unit for pulse-oximetry (SpO2) measurement, and an electrical energy generation and/or stimulation unit. 
     
     
       4. A system as set forth in  claim 1  in which said at least one EMI detector is selected from an edge detector, a level detector, a peak amplitude detector, a peak 1 st  time derivative detector, a peak 2 nd  time derivative detector, a detector for measuring the time interval between the peak EMI amplitude and at least one time derivative, and a detector for measuring the time interval between the peak 1 st  derivative and the peak 2 nd  derivative. 
     
     
       5. A system as set forth in  claim 1  in which said at least one processing element for minimizing said EMI performs at least one operation selected from complete EMI blanking, partial EMI blanking, EMI clipping, EMI attenuation, and EMI filtering. 
     
     
       6. A system as set forth in  claim 1  which includes at least one wireless transmitter for transmitting said physiological data and at least one wireless receiving station for receiving said physiological data from said at least one wireless transmitter. 
     
     
       7. A system as set forth in  claim 1  which includes at least one device selected from defibrillator, cardiac pacing device and monitoring device in said nonmagnetic enclosure. 
     
     
       8. A system as set forth in  claim 1  in which said interface module includes at least one mode of switching of the direction of the impedance-testing electrical current, wherein said switching is selected from: (i) manual switching; (ii) switching at constant time intervals; (iii) switching at time intervals that are tailored to the heart rate of a subject; (iv) switching at time intervals tailored to the breathing movements of a subject; (v) switching at time intervals synchronized with the MRI scanner operation; and (vi) switching at custom time intervals selected by a user. 
     
     
       9. A system as set forth in  claim 1  wherein said at least one processing element is selected from:
 a. at least one delay line for holding said at least one signal during the time required for EMI detection; 
 b. at least one switch for performing at least two operations on the output signal from said at least one EMI detector, wherein said operations are selected from:
 i. passing said output signal from said at least one EMI detector to at least one data-acquisition element during the time intervals in which no EMI is detected; and 
 ii. discarding said output signal during the time intervals in which EMI is detected; 
 
 c. at least one element for regulating the switching-on delay of said at least one switch after EMI is detected, which determines the duration of the discarded segment of said at least one signal during EMI periods; 
 d. at least one sample-and-hold element for holding the last value of said at least one signal preceding the time interval in which said EMI is detected; and 
 e. at least one filter element selected from:
 i. an RF filter respecting the Larmor frequency of the magnetic-field source generating said EMI; and 
 ii. a low-pass filter respecting the difference between the frequency of said EMI and said physiological data for filtering residual noise and EMI from said at least one signal. 
 
 
     
     
       10. A system as set forth in  claim 9  in which said at least one EMI detector is selected from an edge detector, a level detector, a peak amplitude detector, a peak 1 st  time derivative detector, a peak 2 nd  time derivative detector, a detector for measuring the time interval between the peak EMI amplitude and at least one time derivative, and a detector for measuring the time interval between the peak 1 st  derivative and the peak 2 nd  derivative. 
     
     
       11. A system as set forth in  claim 9  in which said at least one processing element for minimizing said EMI performs at least one operation selected from complete EMI blanking, partial EMI blanking, EMI clipping, EMI attenuation, and EMI filtering. 
     
     
       12. A system as set forth in  claim 9  in which said at least one sensor is selected from an ECG sensor, an EMG sensor, an EEG sensor, a blood-pressure sensor, a pulse-oximetry sensor, and an accelerometer sensor. 
     
     
       13. A system adapted for at least one health-related application selected from the physiological monitoring of a subject's health data, cardiac defibrillation, and pacing in the presence of EMI generated by an MRI scanner during an MRI scan of said subject, said system comprising:
 a substantially nonmagnetic enclosure; 
 at least one sensor adapted for collecting at least one signal containing physiological data from the body of said subject; 
 at least one adapter for connecting said body of a subject to at least one device selected from a defibrillator, a cardiac pacing device, and a monitoring device; 
 an interface module in said nonmagnetic enclosure containing at least one EMI detector based on at least one time-domain feature having a different range of values for EMI compared with the range of values of said time-domain feature for said physiological data, to identify EMI within said at least one signal; and 
 at least one processing element for minimizing said EMI within the time intervals in which said EMI is detected; 
 wherein said at least one processing element includes at least one element selected from: 
 a. at least one delay line for holding said at least one signal during the time required for EMI detection; 
 b. at least one switch for performing at least two operations on the output signal from said at least one EMI detector, wherein said operations are selected from:
 i. passing said output signal from said at least one EMI detector to at least one data-acquisition element during the time intervals in which no EMI is detected; and 
 ii. discarding said output signal during the time intervals in which EMI is detected; 
 
 c. at least one element for regulating the switching-on delay of said at least one switch after EMI is detected, which determines the duration of the discarded segment of said at least one signal during EMI periods; 
 d. at least one sample-and-hold element for holding the last value of said at least one signal preceding the time interval in which said EMI is detected; and 
 e. at least one filter element selected from:
 i. an RF filter respecting the Larmor frequency of the magnetic-field source generating said EMI; and 
 ii. a low-pass filter respecting the difference between the frequency of said EMI and said physiological data for filtering residual noise and EMI from said at least one signal. 
 
 
     
     
       14. A system as set forth in  claim 13  in which said at least one EMI detector is selected from an edge detector, a level detector, a peak amplitude detector, a peak 1 st  time derivative detector, a peak 2 nd  time derivative detector, a detector for measuring the time interval between the peak EMI amplitude and at least one time derivative, and a detector for measuring the time interval between the peak 1 st  derivative and the peak 2 nd  derivative. 
     
     
       15. A system as set forth in  claim 13  in which said at least one processing element for minimizing said EMI performs at least one operation selected from: complete EMI blanking, partial EMI blanking, EMI clipping, EMI attenuation, and EMI filtering. 
     
     
       16. A system as set forth in  claim 13  in which said at least one sensor is selected from an ECG sensor, an EMG sensor, an EEG sensor, a blood-pressure sensor, a pulse-oximetry sensor, and an accelerometer sensor. 
     
     
       17. A system adapted for performing at least one operation selected from external cardiac defibrillation, cardiac pacing, and physiological monitoring in an MRI environment, said system comprising:
 a substantially nonmagnetic enclosure; 
 at least one sensor adapted for collecting at least one signal containing physiological data from the body of a subject; 
 an interface module containing at least one EMI detector based on at least one time-domain feature having a different range of values for EMI compared with the range of values of said time-domain feature for said physiological data, to identify EMI within said at least one signal; and 
 at least one processing element for minimizing said EMI within the time intervals in which said EMI is detected; 
 wherein said at least one processing element is selected from: 
 a. at least one delay line for holding said at least one signal during the time required for EMI detection; 
 b. at least one switch for performing at least two operations on the output signal from said at least one EMI detector, wherein said operations are selected from:
 i. passing said output signal from said at least one EMI detector to at least one data-acquisition element during the time intervals in which no EMI is detected; and 
 ii. discarding said output signal during the time intervals in which EMI is detected; 
 
 c. at least one element for regulating the switching-on delay of said at least one switch after EMI is detected, which determines the duration of the discarded segment of said at least one signal during EMI periods; 
 d. at least one sample-and-hold element for holding the last value of said at least one signal preceding the time interval in which said EMI is detected; and 
 e. at least one filter element selected from:
 i. an RF filter respecting the Larmor frequency of the magnetic-field source generating said EMI; and 
 ii. a low-pass filter respecting the difference between the frequency of said EMI and said physiological data for filtering residual noise and EMI from said at least one signal. 
 
 
     
     
       18. A system as set forth in  claim 17  in which said at least one processing element for minimizing said EMI performs at least one operation selected from complete EMI blanking, partial EMI blanking, EMI clipping, EMI attenuation, and EMI filtering. 
     
     
       19. A system as set forth in  claim 17  in which said at least one sensor is selected from an ECG sensor, an EMG sensor, an EEG sensor, a blood-pressure sensor, a pulse-oximetry sensor, and an accelerometer sensor. 
     
     
       20. A system as set forth in  claim 17  in which said at least one EMI detector is selected from an edge detector, a level detector, a peak amplitude detector, a peak 1 st  time derivative detector, a peak 2 nd  time derivative detector, a detector for measuring the time interval between the peak EMI amplitude and at least one time derivative, and a detector for measuring the time interval between the peak 1 st  derivative and the peak 2 nd  derivative.